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Re: [PATCH v3 20/26] DAX/unmap virtiofsd: Parse unmappable elements
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH v3 20/26] DAX/unmap virtiofsd: Parse unmappable elements |
Date: |
Thu, 6 May 2021 16:23:49 +0100 |
On Wed, Apr 28, 2021 at 12:00:54PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> For some read/writes the virtio queue elements are unmappable by
> the daemon; these are cases where the data is to be read/written
> from non-RAM. In viritofs's case this is typically a direct read/write
s/viritofs/virtiofs/
> into an mmap'd DAX file also on virtiofs (possibly on another instance).
>
> When we receive a virtio queue element, check that we have enough
> mappable data to handle the headers. Make a note of the number of
> unmappable 'in' entries (ie. for read data back to the VMM),
> and flag the fuse_bufvec for 'out' entries with a new flag
> FUSE_BUF_PHYS_ADDR.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> with fix by:
> Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
> ---
> tools/virtiofsd/buffer.c | 4 +-
> tools/virtiofsd/fuse_common.h | 7 ++
> tools/virtiofsd/fuse_virtio.c | 230 ++++++++++++++++++++++++----------
> 3 files changed, 173 insertions(+), 68 deletions(-)
>
> diff --git a/tools/virtiofsd/buffer.c b/tools/virtiofsd/buffer.c
> index 874f01c488..1a050aa441 100644
> --- a/tools/virtiofsd/buffer.c
> +++ b/tools/virtiofsd/buffer.c
> @@ -77,6 +77,7 @@ static ssize_t fuse_buf_write(const struct fuse_buf *dst,
> size_t dst_off,
> ssize_t res = 0;
> size_t copied = 0;
>
> + assert(!(src->flags & FUSE_BUF_PHYS_ADDR));
> while (len) {
> if (dst->flags & FUSE_BUF_FD_SEEK) {
> res = pwrite(dst->fd, (char *)src->mem + src_off, len,
> @@ -272,7 +273,8 @@ ssize_t fuse_buf_copy(struct fuse_bufvec *dstv, struct
> fuse_bufvec *srcv)
> * process
> */
> for (i = 0; i < srcv->count; i++) {
> - if (srcv->buf[i].flags & FUSE_BUF_IS_FD) {
> + if ((srcv->buf[i].flags & FUSE_BUF_PHYS_ADDR) ||
> + (srcv->buf[i].flags & FUSE_BUF_IS_FD)) {
> break;
> }
> }
> diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h
> index fa9671872e..af43cf19f9 100644
> --- a/tools/virtiofsd/fuse_common.h
> +++ b/tools/virtiofsd/fuse_common.h
> @@ -626,6 +626,13 @@ enum fuse_buf_flags {
> * detected.
> */
> FUSE_BUF_FD_RETRY = (1 << 3),
> +
> + /**
> + * The addresses in the iovec represent guest physical addresses
> + * that can't be mapped by the daemon process.
> + * IO must be bounced back to the VMM to do it.
> + */
> + FUSE_BUF_PHYS_ADDR = (1 << 4),
Based on the previous patch this is not a gpa, it's an IOVA. Depending
on the virtiofs device's DMA address space in QEMU this might be the
same as guest physical addresses but there could also be vIOMMU
translation (see the address_space_translate() call in the patch that
implemented the IO slave command).
Maybe virtiofs + vIOMMU has never been tested though... I'm not sure it
works today.
If you want to leave it as is, feel free:
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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